For a fibre optical link, you may need AGC to keep wayward RF, optical, and video signals within acceptable bounds
http://www.edn.com/archives/1998/020298/03cs.htm
http://acept.la.asu.edu/courses/phs110/expmts/exp13a.html
converting the current output of a wideband photodetector to a voltage, minimizing noise, and achieving the desired frequency response can tax the patience of even an experienced designer
http://www.edn.com/archives/1996/070496/14df3.htm
describes PIR detector operation
http://www.glolab.com./pirparts/infrared.html
how they works and other documents.
http://www.misty.com/~don/irfilter.html
Newsarticle about laser diodes.
http://margo.student.utwente.nl/el/misc/laserdio.zip
all about liquid crystal display.
http://margo.student.utwente.nl/el/misc/lcd_faq.zip